1. Field of the Invention
The present invention is directed toward the field of manufacturing integrated circuits. The invention is more particularly directed toward an improved method and apparatus for introducing process and purge material in a deposition process system.
2. Description of the Related Art
Presently, aluminum is widely employed in integrated circuits as an interconnect, such as plugs and vias. However, higher device densities, faster operating frequencies, and larger die sizes have created a need for a metal with lower resistivity than aluminum to be used in interconnect structures. The lower resistivity of copper makes it an attractive candidate for replacing aluminum.
There are two well established techniques for depositing copper, chemical vapor deposition (xe2x80x9cCVDxe2x80x9d) and physical vapor deposition (xe2x80x9cPVDxe2x80x9d). A CVD process is desirable because it provides for a more conformally deposited layer. For example, chemical vapor deposition of copper is achieved by using a precursor known as CUPRASELECT(copyright), which has the formula Cu(hfac)L. CUPRASELECT(copyright) is a registered trademark of Schumacher of Carlsbad, Calif. The CUPRASELECT(copyright) consists of copper (Cu) bonded to a deposition controlling compound such as (hfac) and a thermal stabilizing compound (L). The (hfac) represents hexafluoroacetylacetonato, and (L) represents a ligand base compound, such as trimethylvinylsilane (xe2x80x9cTMVSxe2x80x9d).
During the CVD of copper using Cu(hfac)L, the precursor is vaporized and flowed into a deposition chamber containing a wafer. In the chamber, the precursor is infused with thermal energy at the wafer""s surface. At the desired temperature the following reaction results:
2 Cu(hfac)Lxe2x86x92Cu+Cu(hfac)2+2Lxe2x80x83xe2x80x83(Eqn. 1)
The resulting copper (Cu) deposits on the upper surface of the wafer. The byproducts of the reaction (i.e., Cu(hfac)2 and (2L) are purged from the chamber which is maintained at a vacuum during wafer processing.
One problem associated with using CUPRASELECT(copyright) for CVD is the delivery of the material from its liquid storage ampoule to the process chamber in which the CVD occurs. Typically, the liquid CUPRASELECT(copyright) must first be vaporized and mixed with a carrier gas such as Argon, Helium or any other inert gas between the ampoule and the process chamber. Vaporizers are incorporated into the delivery system and function by altering one of two environmental conditions (temperature or pressure). Most vaporizers raise the temperature of the precursor to establish the desired state change. Unfortunately, raising the temperature too high can cause breakdown of the precursor and subsequent plating (deposition) in transfer lines between the ampoule and process chamber. One example is a CEM vaporizer manufactured by Bronkhurst of the Netherlands used to vaporize the precursor liquid. Unfortunately, these devices clog after vaporizing only about 50-1500 g of CUPRASELECT(copyright)). For wafer manufacturing applications, the vaporization rate must be repeatable from wafer to wafer.
After vaporization, CUPRASELECT(copyright) is pumped into the process chamber along with the carrier gas such as Argon, Helium or any other inert gas. This pumping action tends to pull a high concentration of TMVS out of the Cupraselect leaving the less stable copper and (hfac) in the transfer lines between the ampoule, delivery system and process chamber. Under these conditions, undesirable plating or deposition is also likely to occur at important locations. For example, plating can occur near the vaporizer, valves, process chamber showerhead orifices and the like. Plating changes the dimensions of these critical system components which degrades performance of the chamber and the resultant deposition layer. Additionally, unwanted plating may flake off during the deposition process which can render a processed wafer faulty or unusable. A maintenance cycle would then have to be run on the process chamber to replace or clean the chamber which reduces wafer throughput.
To provide for repeatable deposition conditions, it is desirable to create the precursor vapor as close to the process chamber as possible to minimize the likelihood of deposition at any point in the delivery system, to reduce the time and cost of purging the process chamber and most importantly, to reduce pressure gradients in the deposition system. Pressure gradients occur when friction forces act upon the vapor (i.e., along the inner surfaces of vessels and conduits through which the vapor travels). Low pressure is desired in the vaporizer because the efficiency of the vaporizer (and thus, throughput) is limited by pressure. Additionally, the components used to deliver the precursor should be minimized so as to reduce cost and facilitate complete purging of the system when so needed.
Accordingly, it is desirable to provide an apparatus and method for improved control of a precursor material in a substrate process system to reduce the likelihood of plating or particle formation within the system as well as increase deposition rate.
The disadvantages associated with the prior art are overcome with the present invention of an apparatus that allows for improved delivery and vaporization of precursor material. Specifically, a deposition system for performing chemical vapor deposition comprising a deposition chamber having a lid and a vaporizer attached to the lid is provided. Additionally, one or more valves are disposed between the lid and the vaporizer to limit the flow of precursor material to the chamber and to improve purging of a precursor material delivery system attached to the vaporizer. The precursor delivery system has one or more conduction lines. One of the conduction lines is a flexible conduction line in the form of a multiple turn coil having a torsional elasticity suitable for allowing detachment of the lid and vaporizer from the chamber without having to break or disassemble a precursor (liquid) conduction line. Preferably, the flexible conduction line is a thirty (30) turn coil having a diameter of approximately three (3) inches fabricated from xe2x85x9xe2x80x3 stainless steel tubing.
Alternately, the flexible conduction line is made from a permeable membrane material such as fluorocarbon compound such as TEFLON(copyright), a fluorocarbon containing compound, or PFA 440-HP which is then encased in a sheath. The sheath is connected at a first end to the vaporizer and at a second end to a pressure control unit via a valve to allow degassing of the conduction lines and space between the conduction lines and sheath.
The deposition system may also contain additional features such as a pre-warm module to warm a precursor material flowing through the conductance lines prior reaching the vaporizer, a shadow plate disposed over a showerhead in the chamber and an precursor material injection system in the chamber. All of these features lead to improved vaporization and deposition rate of the precursor material and allow for lower pressure operating regimes in the chamber. As such, there is a reduced tendency for the precursor material to break down and undesirably deposit or form particles in the system (i.e., anywhere besides on the substrate to be processed). Hence, system reliability and repeatability is improved.